The major focus of this grant application is phospholipase C-gamma1(PLCgamma1), a substrate of nearly all receptor and some non-receptor tyrosine kinases. When activated, this protein mediates the hydrolysis of phosphatidylinositol 4,5-bisphosphate producing second messenger molecules that elevate Ca2+ and activate protein kinase C. Hence, PLC-gamma1 has a potentially significant, but not well elucidated role in growth factor mitogenic signaling. The overall goal of the experiments proposed in this application is to understand PLCgamma1 at the biochemical level (structure/function, membrane translocation, and activation mechanism), as well as its role in signal transduction pathways that control the growth factor-dependent expression of immediate early genes, the process of cell adhesion to substrata, and cell survival. The final phase of the proposed research will use Plcg1 "knockout" mice and embryonic stem cells to explore the role of this gene in erythrogenesis and vasculogenesis. Also, this phase of the project will employ the Cre-lox system to effect a targeted disruption of Plcg1 in the epidermis. The application proposes to use techniques that encompass biochemistry, cell biology, and molecular genetics. The result of these proposed experiments should significantly increase current understanding of how PLCgamma1 participates in growth factor-dependent mitogenesis.